Coated aluminum welding electrode and filler rod

ABSTRACT

A method of manufacturing a welding electrode or filler rod by cleaning the surface of an aluminum wire rod and applying to the cleaned surface an aqueous solution of an alkali metal silicate having a concentration of greater than 0.5 percent for a period of greater than 5 seconds at a temperature in excess of 140*F in order to establish a thin, oxidation resistant reacted silicate coating on the aluminum surface. Subsequently rinsing and drying the coated aluminum wire or rod. The reacted silicate coating is provided in such a fashion that it has a thickness such that the outermost 1,000 angstroms of the aluminum surface has about 0.10 to 1.25 percent silicon. An aluminum welding rod or electrode having a thin reacted oxidation barrier coating on the exterior surface thereof. The oxidation barrier coating is such that the outermost 1,000 angstroms of the wire surface contains about 0.10 to 1.25 percent silicon and preferably about 0.50 to 0.80 percent silicon. The oxidation resistant coated surface is characterized by resistance to appreciable crazing and flaking responsive to deformation of the aluminum wire.

United States Patent Zelley et al.

[ Feb. 12, 1974 1 COATED ALUMINUM WELDING ELECTRODE AND FILLER ROD [75]Inventors: Walter G. Zelley, Lower Burrell;

- William M. Rogerson, New

Kensington, both of Pa.

[73] Assignee: Aluminum Company of America, Pittsburgh, Pa.

[22] Filed: Dec. 27, 1971 [21] App1.No.:212,785

[52] US. Cl 117/202, 117/49, 219/145, 219/146 [51] Int. Cl B23k 35/00,B23k 35/22 [58] Field of Search 117/202, 206, 49; 219/145, 219/146 [56]References Cited UNITED STATES PATENTS 3,558,368 l/197l Zelley 117/493,256,085 6/1966 Hitchings... 75/58 2,785,094 3/1957 Garriott ll7/2062,697,159 l2/l954 Donaheyt... 338/6 2,552,105 5/195] Miller 148/26Primary Examiner-Alfred L. Leavitt Assistant Examiner-M. F EspositoAttorney, Agent, or Firm-Arnold B. Silverman; John P. Taylor [57]ABSTRACT A method of manufacturing a welding electrode or filler rod bycleaning the surface of an aluminum wire rod and applying to the cleanedsurface an aqueous solution of an alkali metal silicate having aconcentration of greater than 0.5 percent for a period of greater than 5seconds at a temperature in excess of l40 F in order to establish athin, oxidation resistant reacted silicate coating on the aluminumsurface. Subsequently rinsing and drying the coated aluminum wire orrod. The reacted silicate coating is provided in such a fashion that ithas a thickness such that the outermost 1,000 angstroms of the aluminumsurface has about 0.10 to 1.25 percent silicon.

An aluminum welding rod or electrode having a thin reacted oxidationbarrier coating on the exterior surface thereof. The oxidation barriercoating is such that the outermost 1,000 angstroms of the wire surfacecontains about 0.10 to 1.25 percent silicon and preferably about 0.50 to0.80 percent silicon. The oxidation resistant coated surface ischaracterized by resistance to appreciable crazing and flakingresponsive to deformation of the aluminum wire.

I 13 Claims, No Drawings COATED ALUMINUM WELDING ELECTRODE AND FILLERROD BACKGROUND OF THE INVENTION 1. Field of the Invention This 7invention relates to aluminum welding electrodes and aluminum fillerrods on the surfaces of which are established oxidation resistantreacted coatings which preserve desirable welding properties even afterstorage thereof in undesirable environments.

2. Description of the Prior Art In both inert-gas tungsten-arc weldingand inert-gas metal-arc welding numerous problems have been encounteredin connection with deterioration of surface characteristics of weldingelectrodes and filler rods as a result of storage of the same in varioustypes of environments.

In inert-gas tungsten-arc welding a tungsten electrode, which issurrounded by a stream of inert gas confined by a nozzle assembly, isemployed. An electrical arc is established between the tungstenelectrode and the material to be joined. It is frequently necessary ordesirable to employ a filler metal which is introduced in the form of analuminum rod or wire.

In inert-gas metal-arc welding a consumable aluminum electrode issurrounded by a stream of inert gas confined by a nozzle assembly. Anelectrical arc is es tablished between the electrode and the material tobe joined. Means are provided to advance the electrode at a controlledspeed proportionate to the rate at which it is consumed.

In both forms of welding it has been found that the surface condition ofthe electrodes and filler rods can be critical to the quality of theresultant weld. Undesired surface characteristics such as oxidationand/or the presence of hydrocarbons or other foreign material canproduce welding defects such as lack of fusion, weld porosity or otherdiscontinuities in the weld. All of these defects can contribute tofailure of the welded joint. In addition, as oxide coatings arebasically electrically insulating in nature, resistance to theestablishment of an electric arc of the desired intensity can beencountered when using the inert-gas metal-arc welding process. Finally,the presence of an outer layer of oxide on the surface of the electrodeor filler rod permits absorption of water which can have a substantialeffect in contributing to undesired weld porosity.

It has been known in such arc welding operations to remove oxide fromthe surface of electrodes and filler rods immediately prior toinitiation of the welding operation. See U. S. Pat. No. 3,194,704, forexample. Such removal has been effected conveniently either by chemicalmeans or mechanical-means. Such a practice complicates the weldingoperation as it requires the end user of the electrode or filler rod tointroduce a preliminary fabricating step prior to the welding operation.In addition, it requires investment in equipment and labor necessary toaccomplish the cleaning operation. All of this has been necessitated asa result of the absence of an effective protective coating for weldingelectrodes and filler rods which will withstand long periods of storagein various environments without permitting the formation of undesiredhydrated oxide.

It has been known to apply precipitated coatings to the exterior surfaceof electrodes and filler rods in an effort to permit storage whileresisting undesired oxide. Precipitated coatings are relatively thickand are characterized by a low aluminum content and high silicon, oxygenand alkali metal (where employed) concentrations. See U. S. Pat. Nos.1,608,775 and 3,256,085. Such approaches, however, have not resulted ina uniform tenaciously bonded coating which will withstand flexing,bending and forming without crazing or flaking. This failure isparticularly significant in view of the fact that electrodes and fillerrods are conventionally provided in the form of wrapped coils whereinthe electrode or rod is deformed during application to the coil, remainsin the deformed position during storage and is deformed once againduring removal from the coil. An additionaldisadvantage of thisapproach, apart from the functional disadvantage, is that an end userconducting a welding operation prefers to see an electrode or filler rodsurface characterized by brightness of the cleaned original metalsurface, as opposed to a glassy coated surface or a dull oxide surfacecovering. Finally, the precipitated coatings have been characterized byundesirable relatively high electrical resistance which tends tointerfere with the welding operation.

A problem which compounds the storage difficulty is that a given type ofwelding electrode or filler rod will generally be supplied to a greatnumber of end users in various geographical locations with variousclimates. As a result, the temperature and humidity of the immediateenvironment within which the product will be stored will vary greatly.It is a characteristic of oxide coated aluminum electrodes and fillerrods that they tend to come to equilibrium with their environment. As aresult, in a hot dry area the oxide film will tend to remain relativelyunchanged, while in a warm humid area there will be a tendency forgrowth of the oxide film. These environmentally induced changes presentyet another potentially troublesome variable which is directly relatedto the quantity of the product, the efficiency of the welding operationand the freedom of the resultant weld from undesired defects.

There remains, therefore, a need for a method of providing an aluminumarc welding electrode and alumi num filler material which are capable ofbeing stored for prolonged periods of time under severe environmentalconditions while resisting oxide formation of the aluminum surface in aneffective fashion. There remains a further need for such a method andthe resulting product which possesses resistance to crazing and flakingwhen subjected to mechanical deformation and provides a tightly bondeduniform continuous coating having relatively low electrical resistance.

SUMMARY OF THE INVENTION The above-described problems have been solvedby the process and resultant product of this invention. The method ofthis invention involves precleaning the surface of an aluminum wire orrod, which may ultimately be employed as an electrode or filler rod. Thecleaned aluminum rod is then subjected to application of an aqueoussolution of an alkali metal silicate having a concentration of greaterthan 0.5 percent for a time period in excess of 5 seconds, at atemperature of about to 2l2F, in order to establish an oxidationresistant reaction product silicate coating on the rod surface. Thecoating is extremely thin and has a thickness such that the outermost1,000 angstroms of the aluminum surface has at least O.l0 percentsilicon and not more than about 1.25 perent silicon. The preferredconcentration is about 0.50 to 0.80 percent silicon 1 within theoutermost 1,000 angstroms of surface. After establishment of thereaction product coating, the rod is subjected to rinsing and subsequentdrying.

Among the preferred alkali metal silicates are sodium silicate,potassium silicate and lithium silicate. The preferred material issodium silicate having an SiO to Na O ratio of about 2:1 to 3.75:1.

In the preferred process of treatment the aqueous solution will beapplied to the rod by immersion of the rod therein for a period of about30 seconds to 2 minutes with the solution having a temperature of about170 to 190F.

The resultant product has an elongated aluminum body of solid crosssectional configuration with a reacted silicate coating on the exteriorthereof such that the outermost 1,000 angstroms of surface contains atleast 0.10 percent silicon and preferably about 0.50 to 0.80 percentsilicon. The reacted coating is characterized by resistance to oxidationand also resistance to appreciable crazing and flaking responsive todeformation of the aluminum rod.

It is an object of this invention to provide a method of establishing areaction coating on an aluminum welding electrode or filler rod whichcoating will be ef fective in resisting oxidation of the electrode orrod surface even during extended storage under potentially troublesomeenvironmental conditions.

It is another object of this invention to provide such a coatedelectrode or rod wherein the reaction coating will be uniform,continuous and tenaciously bonded to the aluminum substrate.

It is another object of this invention to provide such an electrode orfiller rod with a reacted coating which will eliminate the necessity forchemical or mechanical oxidation removal treatments immediately prior toinitiation of arc welding.

It is another object of this invention to provide such .a reactioncoated product which resists absorption of water, hydrocarbons and othermaterials which tend to contribute to weld defects such as lack offushion, porosity and other discontinuities.

It is yet another object of this invention to provide an economicalmeans for establishing the protective reacted silicate coating of thisinvention which coating provides the product with the natural brightappearance of the aluminum article without deterioration of the sameduring extended storage under various environmental conditions.

These and other objects of the invention will be more fully understoodfrom the following description of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For convenience of reference,the term welding rod as used herein shall be employed to refergenerically to metal wire or rods employed in a welding operation eitheras a welding electrode or as a filler rod. The term aluminum as usedherein shall be employed to refer to any grade of aluminum and aluminumbase alloys wherein aluminum consists of not less than 80 percent byweight of the total composition.

The process of this invention is directed toward the establishment of areaction product coating on the exterior of an aluminum welding rod. Asaluminum surfaces, if unprotected, will in most environments tend to besubject to oxidation on exposed surfaces, the initial step in theprocess of the present invention is that of removing surface oxides aswell as oils, greases and other foreign materials. This serves toprovide a freshly cleaned exposed aluminum surface and facilitateestablishment of the reacted corrosion resistant coatingof thisinvention. This cleaning operation may be accomplished by any convenientmeans such as solvent cleaning, non-etching chemical cleaning, etchingchemical cleaning and mechanical cleaning. One preferred means ofeffecting cleaning is the use of a mild alkaline etching chemicaltreatment. A suitable material for such purposes is tetrasodiumpyrophosphate which is preferably employed at elevated temperatures.After cleaning has been accomplished, the exterior surfaces are rinsed,preferably with water, in order to remove any residual cleaningmaterial, oxides and adhered foreign material.

In order to establish the reaction product coating of this invention, anaqueous solution of an alkali metal silicate having a concentration ofgreater than 0.5 percent is applied to the cleaned aluminum rod for aperiod of about 5 seconds to 10 minutes at a temperature of about to212F. This results in establishment of a relatively thin oxidationresisting reacted silicate coating such that the outermost 1,000angstroms of surface of the aluminum rod has at least 0.10 percentsilicon. In obtaining this concentration measurement for the extremelythin reacted coating, it should be noted that the coating is too thin tobe readily stripped for weight determination. It is, however, possibleto determine surface silicon by means of an electron microprobe whichpenetrates the surface coating and possibly penetrates somewhat into thesurface of the aluminum rod. This penetration causes X-rays to beemitted from the coating and the intensity of the-X-ray wave length forsilicon is directly related to and indicative of the siliconconcentration. While the practical upper limit of concentration of thesilicate is the water solubility of the silicate, highly concentratedsolutions tend to result in difficulty in rinsing, an undesirably highdrag-out or removal of the material from solution by the product beingtreated and resultant waste of material. It is, therefore, preferredthat the concentration of the silicate be about 0.5 to 10 percent.Although higher concentrations will function effectively, it generallywill be economically beneficial to remain within the preferred range. Ingeneral, the silicon concentration in the outermost 1,000 angstroms ofsurface should not exceed about 1.25 percent. In a preferred form of theinvention the silicon concentration will be about 0.50 to 0.80 percent.A period of application of the aqeuous solution of at least 5 seconds isrequired. As the solution does not etch the metal surface appreciably orproduce a material change in reacted coating, the prime consideration inselecting a maximum period of time will be economic, as no appreciableadded benefits are obtained after a time period of about 10 minutes. Thepreferred period of application is about 30 seconds to 2 minutes.

With respect to temperature of the solution, a minimum of about 140F isrequired in order to provide an appropriate reacted coating. The upperlimit of temperature would be about 212F as the solution would begin toboil at about that point. It is preferred that the solution be providedat a temperature of about to F.

ln general, it is preferred to apply the aqueous solution to the cleanedaluminum rod by immersing the rod in a bath of the aqueous solution.While other methods, such as spraying, can be employed if desired,immersion remains the preferred method as it tends to contribute togreater uniformity and continuity of the coat- Among the preferredalkali metal silicates for use in the aqueous solution of this inventionare sodium silicate, potassium silicate and lithium silicate. Aspecifically preferred material is sodium silicate having an SiO to Na Oratio of about 2:1 to 3.75:].

After creating the corrosion resistant reacted silicate coating, thealuminum rod is subjected to a rinse, preferably with water, in order toremove any excess aqueous solution therefrom. The aluminum rod is thendried. It is found that the resultant product has a thin reactedsilicate coating which suppresses oxidation growth on the surface of thealuminum rod even after extended storage periods in adverseenvironments. The coating is uniform and continuous. The thin reactedfilm is characterized by a relatively high aluminum content and arelatively low silicon and oxygen content. It will generally besubstantially devoid of the alkali metal. it possesses a desirable lowelectrical resistance on the order of 250 microhms and generally withinthe range of about 200 to 1,500 microhms as measured between 0.5 inchcopper electrodes at 1,000 pounds pressure by means of a Kelvin bridge.Also, the reacted silicate coating permits the natural bright finish ofthe aluminum to be readily observed and preserved during extendedstorage. The reacted coating is such that it will withstand flexing,bending and forming of the aluminum rod without appreciable crazing orflaking.

EXAMPLE In order to verify the effectiveness of the process of thisinvention comparative tests were performed. Two consumable aluminumelectrodes of the type used in inert-gas metal-arc welding wereprovided. The electrodes were composed of 5356 alloy, which is astandard alloy conventionally employed in such uses, and were ofone-sixteenth inch in diameter. One electrode was cleaned for seconds ina gram/liter solution of tetrasodium pyrophosphate at 180F. Thiselectrode was subsequently subjected to a water rinse to remove looseparticles of oxide and foreign materials. This electrode was thentreated with a milliliter/liter solution of sodium disilicate, soldunder the trade designation DuPont 26, at 180F for 60 seconds. Theelectrode was then subjected to a water rinse and dried. The secondelectrode was not treated. These two electrodes were then subjected toan environment maintained at percent relative humidity at F for a periodof twelve weeks, in order to simulate severe storage conditions. Afterthe twelve week exposure, the second electrode showed readily visibleevidence of spotting on the surface which was indicative of undesiredoxidation. The first electrode which had been treated remained uniformlybright. These two welding first and third electrodes. This clearly showsthe effectiveness of the reacted silicate coating of this invention inwithstanding severe environmental conditions during extended storagewhile performing in a fashion equal to that of a fresh unexposed weldingelectrode. 7

The welding rod produced by the process of this invention has anelongated body of substantially solid cross sectional configuration. Areacted oxidation barrier coating on the exterior surface of theelongated body is such that the outermost 1,000 angstroms of surface ofthe welding rod contains at least 0.10 percent silicon. The reactedcoating will have a silicon content of less than about 1.25 percent. Thepreferred silicon content is about 0.50 to 0.80 percent.

The process and product of this invention may be employed with a widerange of aluminum alloys. lt is particularly suitable for those alloysconventionally employed in the manufacture of aluminum electrodes andaluminum filler rods. Alloys frequently used in the manufacture ofaluminum filler rods and electrodes are wrought alloys designated by theAluminum Association (New York, N. Y.) and commonly known as 1100, 1260,2319, 4043, 4047, 4145, 5039, 5154, 5356, 5554, 5556 and 5654, as wellas casting alloys 319, 355 and 356.

It will, therefore, be appreciated that the process of this inventionestablishes a reacted silicate coating on an aluminum welding rod whichcoating is stable, resists oxidation and resists absorption of water andother foreign materials potentially deleterious to the welding operationand the resulting product. In addition, the tenaciously bonded reactedsilicate coating is uniform and continuous. It also resists crazing andflaking responsive to flexing, bending and forming of the welding rod.The coating has a relatively low electrical resistance and permits fullvisual exposure of the bright aluminum surface. All of these propertiesare maintained during long storage under a wide variety of potentiallytroublesome environmental conditions. Finally, the reaction coating ofthis invention may be readily and rapidly created in an economicalfashion by the product manufacturer. This eliminates the need foroxidation removal and other substantial pretreatment on the part of theend user performing the welding operation.

Whereas particular embodiments of the invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details may be made withoutdeparting from the invention as defined in the appended claims.

We claim: 1. A method of manufacturing a welding rod comprisingproviding an elongated aluminum rod, cleaning the surface of saidaluminum rod, applying to said cleaned aluminum rod surface an aqueoussolution of an alkali metal silicate having a concentration greater than0.5 percent for a period of greater than 5 seconds at a temperature ofabout to 212F to establish an oxidation resistant reacted silicatecoating on said aluminum rod surface, rinsing said silicate coatedaluminum rod, and drying said silicate coated aluminum rod. 2. Themethod of claim 1 including providing said aqueous solution with amaterial selected from the group consisting of sodium silicate,potassium silicate and lithium silicate, and

establishing said reacted silicate coating of such a thickness that theoutermost l,000 angstroms of said aluminum rod surface has at least 0.10percent silicon.

3. The method of claim 2 including applying said aqueous solution tosaid aluminum rod by immersion of said aluminum rod in said alkali metalsilicate aqueous solution.

4. The method of claim 2 including establishing said oxidation resistantreacted silicate coating of a thickness such that the outermost 1,000angstroms of said aluminum rod surface has about 0.10 to 1.25 percentsilicon.

5. The method of claim 2 including treating said aluminum rod with anaqueous solution of sodium silicate having an SiO to Na O ratio of about2:1 to 3.75:].

6. The method of claim 4 including applying said aqueous solution tosaid aluminum rod at a temperature of about 170 to 190F for a period ofabout 30 seconds to 2 minutes.

7. The method of claim 5 including rinsing said cleaned aluminum rodsurface with water prior to application of said aqueous solution, and

establishing said oxidation resistant reacted silicate coating of athickness such that the outermost 1,000 angstroms of said aluminum rodsurface has about 0.50 to 0.80 percent silicon.

8. The method of claim 7 including subsequent to rinsing and drying saidreacted silicate coated aluminum rod employing said aluminum rod as aconsumable welding electrode in an inertgas metal-arc welding operationto form a weld characterized by a substantial absence of porosity.

9. The method of claim 7 including subsequent to rinsing and drying saidreacted silicate coated aluminum rod employing said aluminum rod as afiller rod in an inert-gas tungsten-arc welding operation to form a weldcharacterized by a substantial absence of porosity.

10. An aluminum welding rod comprising an elongated body ofsubstantially solid cross sectional configuration,

a reacted oxidation barrier coating on the exterior surface of saidelongated body, and

said oxidation barrier coating being such that the out- I ermost 1,000angstroms of said coated surface contains at least 0.10 percent silicon.

11. The welding rod of claim 10 including said reacted oxidation barriercoating being such that the outermost 1,000 angstroms of said coatedsurface contains about O.l0 to 1.25 percent silicon.

12. The welding rod of claim 11 including said reacted coating beingsubstantially continuous and of substantially uniform thickness, and

said coating being the reaction product of the application of an alkalimetal silicate aqueous solution to the outer surface of said aluminumrod in order to establish a reacted coating substantially devoid ofalkali metal and having the outermost 1,000 angstroms of the coated rodsurface containing about 0.50 to 0.80 percent silicon and said reactedcoating is characterized by resistance to appreciable crazing andflaking responsive to deformation of said aluminum rod.

13. A method of manufacturing a welding rod capable of producing weldscharacterized by a substantial absence of porosity comprising:

a. providing an elongated aluminum rod;

b. cleaning the surface of said aluminum rod with an alkaline etchtreatment;

0. rinsing said cleaned aluminum rod surface with water;

(1. applying to said cleaned and rinsed aluminum surface an aqueoussolution of an alkali metal silicate having a concentration greater than0.5 percent for a period of greater than 5 seconds at a temperature ofabout to 212F to establish an oxidation resistant reacted silicatecoating on said aluminum rod surface;

e. rinsing said silicate coated aluminum rod to remove any excessaqueous alkali metal silicate thereon leaving a thin reacted silicatecoating thereon substantially devoid of alkali metal; and

f. drying said reacted silicate coated alumin um rod.

2. The method of claim 1 including providing said aqueous solution witha material selected from the group consisting of sodium silicate,potassium silicate and lithium silicate, and establishing said reactedsilicate coating of such a thickness that the outermost 1,000 angstromsof said aluminum rod surface has at least 0.10 percent silicon.
 3. Themethod of claim 2 including applying said aqueous solution to saidaluminum rod by immersion of said aluminum rod in said alkali metalsilicate aqueous solution.
 4. The method of claim 2 includingestablishing said oxidation resistant reacted silicate coating of athickness such that the outermost 1,000 angstroms of said aluminum rodsurface has about 0.10 to 1.25 percent silicon.
 5. The method of claim 2including treating said aluminum rod with an aqueous solution of sodiumsilicate having an SiO2 to Na2O ratio of about 2:1 to 3.75:1.
 6. Themethod of claim 4 including applying said aqueous solution to saidaluminum rod at a temperature of about 170* to 190*F for a period ofabout 30 seconds to 2 minutes.
 7. The method of claim 5 includingrinsing said cleaned aluminum rod surface with water prior toapplication of said aqueous solution, and establishing said oxidationresistanT reacted silicate coating of a thickness such that theoutermost 1,000 angstroms of said aluminum rod surface has about 0.50 to0.80 percent silicon.
 8. The method of claim 7 including subsequent torinsing and drying said reacted silicate coated aluminum rod employingsaid aluminum rod as a consumable welding electrode in an inert-gasmetal-arc welding operation to form a weld characterized by asubstantial absence of porosity.
 9. The method of claim 7 includingsubsequent to rinsing and drying said reacted silicate coated aluminumrod employing said aluminum rod as a filler rod in an inert-gastungsten-arc welding operation to form a weld characterized by asubstantial absence of porosity.
 10. An aluminum welding rod comprisingan elongated body of substantially solid cross sectional configuration,a reacted oxidation barrier coating on the exterior surface of saidelongated body, and said oxidation barrier coating being such that theoutermost 1, 000 angstroms of said coated surface contains at least 0.10percent silicon.
 11. The welding rod of claim 10 including said reactedoxidation barrier coating being such that the outermost 1,000 angstromsof said coated surface contains about 0.10 to 1.25 percent silicon. 12.The welding rod of claim 11 including said reacted coating beingsubstantially continuous and of substantially uniform thickness, andsaid coating being the reaction product of the application of an alkalimetal silicate aqueous solution to the outer surface of said aluminumrod in order to establish a reacted coating substantially devoid ofalkali metal and having the outermost 1,000 angstroms of the coated rodsurface containing about 0.50 to 0.80 percent silicon and said reactedcoating is characterized by resistance to appreciable crazing andflaking responsive to deformation of said aluminum rod.
 13. A method ofmanufacturing a welding rod capable of producing welds characterized bya substantial absence of porosity comprising: a. providing an elongatedaluminum rod; b. cleaning the surface of said aluminum rod with analkaline etch treatment; c. rinsing said cleaned aluminum rod surfacewith water; d. applying to said cleaned and rinsed aluminum surface anaqueous solution of an alkali metal silicate having a concentrationgreater than 0.5 percent for a period of greater than 5 seconds at atemperature of about 140* to 212*F to establish an oxidation resistantreacted silicate coating on said aluminum rod surface; e. rinsing saidsilicate coated aluminum rod to remove any excess aqueous alkali metalsilicate thereon leaving a thin reacted silicate coating thereonsubstantially devoid of alkali metal; and f. drying said reactedsilicate coated aluminum rod.